Variable drive potentiometer



March 17, 1953 c. J. CLEMENTS, JR 2,632,075

VARIABLE DRIVE POTENTIOMETER Filed Oct. 15, 1951 2 SHEETSSHEET l ZERO RESlSTANCE IN THESE SECTIONS so vour -5o vour INPUT NQ'I \NPUT No.2.

PHASE 3 '5 Re PHASE 1 as K PHASE 2 197% REV. MECH. ROTATION IINVENTOR [LANE/VIE J [a EMENFE JR.

Mao/4 BY 69 c/ 92% 4951x 75 March 17, 1953 c. J. CLEMENTS, JR 2,632,076

VARIABLE DRIVE POTENTIOMETER 2 SHEETS-SHEET 2 Filed Oct. 15 1951 INVENTOR ZZARf/VZEJ [z fMf/VFZ JR jzdfgr cw 495N715 Patented Mar. 17, 1953 VARIABLE DRIVE POTENTIOMETER Clarence J. Clements, J r., Silver Spring, Md., assignor to Engineering and Research Corporation, River-dale, Md.

Application October 15, 1951, Serial No. 251,387

4 Claims.

The present invention relates in general to variable resistors or potentiometers, but more in particular to variable resistors or potentiometers in which the resistance element has the form of a compound helix. The object of the invention is to produce a new and improved variable resistor of this character.

More particularly my invention comprehends a variable resistor or potentiometer which is so constructed so as to enable its resistance or potential to be varied by more than one mechanical input.

The invention also comprehends a variable resistor or potentiometer which is so constructed as to permit its mechanical input shaft to be turned through a considerable number of revolutions without affecting the devices initial resistance or potential and upon further rotation, after this initial predetermined number of turns of the in put shaft, varies the resistance or potential linearly or otherwise with an additional predetermined number of revolutions of the shaft. If desired, provision for an additional number of revolutions or phase of operation may be provided, during which the resistance or potential would remain the same as established at the termination of the variable phase.

The foregoing and other features of the invention will be more fully described hereinafter and clarified by the accompanying drawings, in which Fig. l is an electro-mecham'cal schematic of the device wired as a potentiometer.

Fig. 2 is an end view of the device.

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2.

Fig. 4 is a sectional view taken on line 4-4 of Fig. 3.

Fig. 5 is a sectional view taken on line 5-5 of Fig. 3.

Referring to the drawings, Fig. 1 shows the three phases of operation I of the device when wired as a potentiometer. As may be seen from the schematic, assuming input #I to be equal to +50 volts and input #2 to be equal to 50 volts, the voltage taken from right to left would be as follows: during phase I the wiper voltage would be 50 volts due to the substantially zero resistance of the conductor upon which the wiper is riding during this phase. As the wiper embarks upon phase 2 of its travel, it travels over a resistance element of compound helical form and the voltage taken off by the wiper will vary from 50 volts to zero volts at the middle of its travel in phase 2, at which point the plus and minus electrical inputs to opposite ends of the potentiometer will cancel each other out. It therefore follows that the voltage taken off by the wiper during the remainder of its travel in phase 2 will vary from zero to +50 volts. Due to the fact that the surface upon which the wiper rides, during .phase 3 of its travel, has substantially zero resistance the wiper take off voltage during this phase will remain a constant +50 volts.

Fig. 2 is an end view of the device and Fig. 3 is a sectional view of the device taken on line 3-3 of Fig. 2 in which I is the case of the potentiometer which is made of phenolic tubing or some other non conductor, 2 and 3 are the end covers which contain ball bearings 4 and 5 in which shafts 6 and 1 of spider frame 8 revolve.

Spider frame 8 is provided with ball bearings 9 and I0 in which lead screw II is mounted. Lead screw I does not have a constant lead but rather is divided into three sectionsl2, l3 and |4,a1l of which are connected and revolve as a unit, sections l2 and !4 having a lead, for instance, of one twenty second of an inch per revolution, and section I3 a lead of one quarter inch per revolution. Gear I5 is pinned to the right hand end of lead screw l l and meshes with gear l6 which is cut on the inside of end plate 3.

A rider H is mounted on lead screw II and carries pin I8 (Fig. 4) in a hole in the body of rider H. Pin 18 has a small projection l9 which engages the groove in lead screw H. Pin I8 is retained in the body of the rider by a washer head screw 20.

At the lower edge of the rider two miniature ball bearings 28 and 29 are mounted, whose outer races bear on spider frame 8. The purpose of these bearings is to prevent rider I! from revolv ing with lead screw I l.

Rider I! also carries a spring contact arm 2| upon which is mounted contact 22. The contact arm is insulated from the rider by a phenolic block 23. One end of an insulated wire 24 is soldered to contact arm 2|, the other end of the wire being soldered to contact arm 25 (Fig. 5) upon which is mounted contact 26. This contact arm is mounted on insulator 21, which in turn is mounted on the left hand end of spider frame 8. A resistance element 30 is mounted in a helical groove on the inside of case I This resistance element is in the form of a compound helix; that is, it is comprised of thin resistance wire wound in helical fashion upon an elongated insulated core which then in turn is formed into a helix.

To the right of resistance element 30 is mounted a sleeve 31 which is made of coin silver or some other metal of high electrical conductivity. To the left of resistance element 30 is a silver sleeve 3 32 similar to 3|. To the left of 32 is a shorter silver sleeve 33 upon which contact 26 (Fig.

bears.

When the device is used as a potentiometer, as

outlined in the discussion of the schematic shown 5 a similar electrical connection (not shown) would be made between sleeve 33 and slip ring 31,

Slip rings 35, 36 and 37 could be replaced by plain lead wires in the event that gear 3'8,--which input as well as shaft tpr l.

'I'he device. will, therefore, operate as follows; iwhen input shaft 6 or '5 is turned, spider frame 18 also rotates causing lead screw ll to travel an are about gear it on the inside of cover 3. As shown in Fig. 3, gear l5 which is pinned to "lead screw H meshes with. gear It. Gearl3 will then cause lead screw l l to rotate and propel the rider I! along the length of the screw.

It has now become apparent how the operation described in the explanation of the schematic in Fig. 1 is accomplished. Let us assume that the rider and its accompanying contact 22 begin their excursion at the extreme right hand end of portion I2 of lead screw l; as the input shaft 1 is turned the contact 22 will travel in a helical path along the inside surface of sleeve 3! towards the left. Assuming portion [2 of the lead screw to have a lead of one twenty second of an inch per revolution and gear I5 to have a pitch diameter twice that of gear IS, the pitch of the helix traced by contact 22 on the inner surface of sleeve 31 will be one forty fourth of an inch per revolution. Thus it will be seen that the 81%. revolutions of the shaft 1 in phase 1 will only cause contact 22 to travel approximately two inches. vWhen rider ll reachesthe end of portion I2 of the lead screw it begins to follow portion l3 of the lead screw which might have a lead of one quarter inch per revolution and would cause the contact 22 to follow the helical convolutions of resistance element 3i) which would have a pitch of one eighth inch per turn. After the contact 22 has tracedthe convolutions of resistance element 3!! to itslefit hand end, section i3 of-the lead screw ends and the propulsion of the'rider I? and contact 22 is then undertaken by section M of the lead screw. Asdiscussed previously, section I4 is identical to section i2 and therefore the travel of rider I"! along these two sections would be the same.

Slip rings 35, 3E and 3? need only beused when the differential feature of the device isemployed. In the event that the resistance or potential of the device is required to be varied by two mechanical inputs shafts 6 and I would be mounted in bearings (not shown) and another gear (not shown) would be meshed with gears 38 on cover 3. Upon rotation of this auxiliary gear the case I of the device is caused to turn and through gears l5 and I6 and lead screw II the rider I! would be caused to travel axially. The case could 'of course be rotated at the-sameztime as shaft 1.

It is of oourseobviousf thatxresistance element 3|] need not be linear but that selected sections of its length could be of a different value of resistance perinch than other sections.

It is also obvious that sleeves 3| and 32 could be 'replaced .by resistance elements of various types of construction.

i' Iido notlirhitmyself to the precise apparatus shown and described above as this is to be con- "sidered merel' 'asa re resentative form of m is afiixed to cover 3, was not used as a mechanical I y p y invention.

What I claim is:

. 1. .A mechanicaldevice consisting of a cylindricalcasingwith ,end caps, a central shaft, a spider frame carried by saidshaft, a lead screw rotat :ably attached to said spider frame, a first gear afiixed to one end of the. lead screw. .asecond gear concentric with the central shaft affixed to the inner surface of one end cap and meshing with the first gear, a rider mounted on andengaging the lead screw suitably restrained from rotating with the lead screw, a contact arm.mounted on said rider a contact mounted on said arm and bearing on the innersurface of the. cylindrical casing so that upon rotation of the central shaft the contact traces a helical path along the inner surface of the cylindrical case.

2. A device as claimed in claim 1 wherein the length of the leadscrew is divided into a plurality ofsections of varyingxlead.

3. A device as claimed in claim ,1 wherein a helical resistance. element is affixed 'to the inner surfaceof the cylindrical case to correspond to the helical path tracedby the contact.

4. A device as claimedin claim 1 wherein the lead screw is axially divided into three sections the center section 'being'of a greater lead than the end sections, a helical resistance element vanixed to the inner surface of the casing opposite the center section of the lead screw, cylindrical metal sleeves afiixed to the inner surface of the casing opposite the end portions of the lead screw, each of said sleeves-being attached to one extremity of the'resistance element.

-. CLARENCE J. CLEMENTS, JR.

REFERENCES CITED 'I he following references are of record in the file of thispatentr r UNITED STATES PATENTS 

